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Euarchontan Opsin Variation Brings New Focus to Primate Origins.

ABSTRACT: Debate on the adaptive origins of primates has long focused on the functional ecology of the primate visual system. For example, it is hypothesized that variable expression of short- (SWS1) and middle-to-long-wavelength sensitive (M/LWS) opsins, which confer color vision, can be used to infer ancestral activity patterns and therefore selective ecological pressures. A problem with this approach is that opsin gene variation is incompletely known in the grandorder Euarchonta, that is, the orders Scandentia (treeshrews), Dermoptera (colugos), and Primates. The ancestral state of primate color vision is therefore uncertain. Here, we report on the genes (OPN1SW and OPN1LW) that encode SWS1 and M/LWS opsins in seven species of treeshrew, including the sole nocturnal scandentian Ptilocercus lowii. In addition, we examined the opsin genes of the Central American woolly opossum (Caluromys derbianus), an enduring ecological analogue in the debate on primate origins. Our results indicate: 1) retention of ultraviolet (UV) visual sensitivity in C. derbianus and a shift from UV to blue spectral sensitivities at the base of Euarchonta; 2) ancient pseudogenization of OPN1SW in the ancestors of P. lowii, but a signature of purifying selection in those of C. derbianus; and, 3) the absence of OPN1LW polymorphism among diurnal treeshrews. These findings suggest functional variation in the color vision of nocturnal mammals and a distinctive visual ecology of early primates, perhaps one that demanded greater spatial resolution under light levels that could support cone-mediated color discrimination.

SUBMITTER: Melin AD

PROVIDER: S-EPMC4776711 | biostudies-literature | 2016 Apr

REPOSITORIES: biostudies-literature

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Euarchontan Opsin Variation Brings New Focus to Primate Origins.

Melin Amanda D AD Wells Konstans K Moritz Gillian L GL Kistler Logan L Orkin Joseph D JD Timm Robert M RM Bernard Henry H Lakim Maklarin B MB Perry George H GH Kawamura Shoji S Dominy Nathaniel J NJ

Molecular biology and evolution 20160106 4

Debate on the adaptive origins of primates has long focused on the functional ecology of the primate visual system. For example, it is hypothesized that variable expression of short- (SWS1) and middle-to-long-wavelength sensitive (M/LWS) opsins, which confer color vision, can be used to infer ancestral activity patterns and therefore selective ecological pressures. A problem with this approach is that opsin gene variation is incompletely known in the grandorder Euarchonta, that is, the orders Sc ...[more]

PMID: 26739880

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Project description:Sensory adaptation to the local environment can contribute to speciation. Aquatic environments are well suited for studying this process: The natural attenuation of light through water results in heterogeneous light environments, to which vision-dependent species must adapt for communication and survival. Here, we study visual adaptation in sympatric Pundamilia cichlids from southeastern Lake Victoria. Species with blue or red male nuptial coloration co-occur at many rocky islands but tend to be depth-differentiated, entailing different visual habitats, more strongly at some islands than others. Divergent visual adaptation to these environments has been implicated as a major factor in the divergence of P. pundamilia and P. nyererei, as they show consistent differentiation in the long-wavelength-sensitive visual pigment gene sequence (LWS opsin). In addition to sequence variation, variation in the opsin gene expression levels may contribute to visual adaptation. We characterized opsin gene expression and LWS genotype across Pundamilia populations inhabiting turbid and clear waters, to examine how different mechanisms of visual tuning contribute to visual adaptation. As predicted, the short-wavelength-sensitive opsin (SWS2b) was expressed exclusively in a population from clear water. Contrary to prediction however, expression levels of the other opsins were species- and island-dependent and did not align with species differences in LWS genotype. Specifically, in two locations with turbid water, the shallow-water dwelling blue species expressed more LWS and less RH2A than the deeper-dwelling red species, while the opposite pattern occurred in the two locations with clear water. Visual modeling suggests that the observed distribution of opsin expression profiles and LWS genotypes does not maximize visual performance, implying the involvement of additional visual tuning mechanisms and/or incomplete adaptation.Open research badgeThis article has earned an Open Data Badge for making publicly available the digitally-shareable data necessary to reproduce the reported results. The data is available at https://hdl.handle.net/10411/I1IUUQ.

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Euarchontan Opsin Variation Brings New Focus to Primate Origins.

Publications

Euarchontan Opsin Variation Brings New Focus to Primate Origins.

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